kefB is annotated as a potassium/proton antiporter in M. tuberculosis. There have been divergent reports on the involvement of KefB in phagosomal maturation in M. bovis BCG and no investigation has been carried out on its role in M. tuberculosis, the pathogenic species responsible for causing tuberculosis. This study was taken up to ascertain the involvement of KefB in the growth of M. tuberculosis and its role in phagosomal maturation and survival of the pathogen in guinea pigs. Our findings show that kefB mutant of M. tuberculosis (MtbΔkefB) was impaired i) for growth in high concentrations of potassium and ii) in arresting phagosomal acidification. However, the disruption of kefB had no adverse effect on the survival of M. tuberculosis in macrophages as well as in guinea pigs suggesting that the role of KefB in phagosomal acidification is unrelated to the survival of the pathogen in the host.